1. Field of the Invention
The present invention relates to an image read apparatus and an image read method. More particularly, the present invention relates to an image read apparatus and method to prevent generation of a black streak and the like in the readout image caused by dust or foreign objects in an image read apparatus that reads out an image by moving a document with respect to a reader.
2. Description of the Related Art
In a conventional image read apparatus such as a digital copy machine, the so-called flow-shooting technique is employed. By this technique, an image is read out by moving the document original with respect to a fixed reader. The reader itself is not moved. In the case where dust is located at the readout position, the reader will constantly read out also the dust during the flow of the document. The dust will be recognized as a black streak or white streak (the terms xe2x80x9cblack streakxe2x80x9d and xe2x80x9cwhite streakxe2x80x9d also include dotted lines and the like), whereby a black streak or a white streak will be generated in the sub-scanning direction of the readout image, and in turn, in the output image.
To solve this problem, Japanese Patent Laying-Open No. 6-70099 discloses the technique set forth in the following.
FIG. 15 is a block diagram showing a schematic structure of an image read apparatus of the prior art. Referring to FIG. 15, the image read apparatus of the conventional art includes a plurality of lines of a CCD (Charge Coupled Device) 151 to read the same position of a document with a predetermined time difference, a line buffer memory 152 temporarily storing data output from CCD 151 to cancel the time difference between each CCD to obtain data corresponding to the same position in the document, and a majority decision calculation unit 153 to carry out decision by majority of data for the input same position.
Majority decision calculation unit 153 outputs the most frequent value out of the input data as the proper image data. Therefore, the data corresponding to the readout of dust is not output as image data. Thus, generation of a black streak corresponding to dust is prevented.
This conventional image read apparatus obtains the correct binary image data by calculating the majority of the binary data. Application thereof is difficult in the case of multi-bit data.
It is to be noted that this conventional image read apparatus simply employs any one data out of the data output from a plurality of CCD 151. The usage of the plurality of CCD 151 provides only the advantage of preventing generation of a black streak, and could not improve the picture quality of the entire image.
An object of the present invention is to provide an image read apparatus and method that can prevent generation of a black or white streak on a readout image caused by the presence of dust at the readout position, and that can improve the picture quality of the entire image.
The above object of the present invention can be achieved by an image read apparatus of the present invention.
According to an aspect of the present invention, an image read apparatus includes an image reader reading out an image while a document is moved. The image reader includes a plurality of fixed read units having a different readout position with respect to the moving direction of a document. The image read apparatus also includes a determination unit determining unnecessary data from the read data of each read unit, and an averaging unit averaging the read data of each read unit other than the unnecessary data.
According to the present invention, unnecessary data corresponding the readout of dust out of the readout data from the plurality of read units is determined, and the read data other than the determined unnecessary data are averaged. Thus, an image read apparatus that can prevent generation of a black or white streak on a readout image caused by the presence of dust at the read position, and that can improve the picture quality of the entire image with the read data averaged can be provided.
Preferably, the averaging unit adds the read data of each reader for averaging. The averaging process is facilitated since the read data of each read unit is added and averaged.
Preferably, the determination unit determines the unnecessary data by comparing the value of the read data of the read unit with a predetermined threshold value.
Thus, unnecessary data can be determined easily and appropriately since unnecessary data is determined according to comparison with a predetermined threshold value.
Preferably, the read unit is formed of a line sensor extending in a direction orthogonal to the moving direction of a document.
Since the image of a document is read out by a line sensor extending in a direction orthogonal to the moving direction of a document, an image can be read out at the most efficient sensor configuration.
According to another aspect of the present invention, an image read method includes the step of reading out an image by an image reader while a document is moved. The image reader includes a plurality of fixed read units having a different readout position in the moving direction of a document. The image read method includes the step of determining unnecessary data from read data of each read unit, and the step of averaging the read data of each read unit other than unnecessary data.
According to the present invention, unnecessary data corresponding to dust readout is determined out of the read data from the plurality of read units, and the read data other than the determined unnecessary data are averaged. Thus, an image read method that can prevent generation of a black or white streak on a readout image caused by the presence of dust at a read position, and that can improve the picture quality of the entire image with the read data averaged can be provided.
Preferably, the averaging step is carried out by adding the read data of each read unit.
Averaging is facilitated since the read data of each read unit is added and averaged.
Preferably, the determination step determines unnecessary data by comparing the value of the read data of the read unit with a predetermined threshold value.
Accordingly, unnecessary data can be determined easily and appropriately since unnecessary data is determined according to comparison with the predetermined threshold value.
Preferably, the read unit includes a line sensor extending in a direction orthogonal to the moving direction of the document.
Since the image of a document is read by a line sensor extending in a direction orthogonal to the moving direction of the document, an image can be read out at the most efficient sensor configuration.
According to another aspect of the present invention, an image read apparatus includes an image reader reading out an image with a document moved, a mode set unit setting at least one mode from a plurality of modes, a threshold value set unit setting a threshold value according to the mode set by the mode set unit, and a determination unit determining unnecessary data from the data read out from the image reader by comparing the value of the read data of the image reader with the threshold value set by the threshold value set unit.
According to the present invention, unnecessary data is determined from the data read out from the image reader based on the comparison result with a threshold value appropriately set according to the mode. Therefore, unnecessary data can be determined appropriately to prevent generation of a black or white streak.
Preferably, the image read apparatus further includes a data table in which a plurality of modes and a threshold value are stored in correspondence. The threshold value set unit refers to the data table to set the threshold value.
Since a threshold value corresponding to the mode is prestored as a data table, an appropriate threshold value can be set easily.
Preferably, the plurality of modes include at least one of a plurality of modes set according to the type of the document image, a plurality of modes set according to the amount of exposure of the image reader, and a plurality of modes set according to the type of dust adhering to the image reader.
Accordingly, a threshold value is set according to parameters that greatly affect dust detection such as the type of document image, the amount of exposure of the image reader, and the type of dust. Thus, a more appropriate threshold value can be set to prevent generation of a black or white streak.
Preferably, the image reader includes a plurality of fixed read units having a different readout position with respect to the moving direction of the document.
A document is read out by a plurality of fixed read units having a different readout position with respect to the moving direction of the document. Therefore, a plurality of read data can be obtained to determine unnecessary data therefrom more appropriately.
Preferably, the image unit includes a line sensor extending in a direction orthogonal to the moving direction of a document.
Since the image of a document is read out by a line sensor extending in a direction orthogonal to the moving direction of the original, an image can be read out at the most efficient sensor configuration.
According to still another aspect of the present invention, an image read method includes the step of reading out an image by an image reader with a document moved, the step of setting at least one mode from a plurality of modes, the step of setting a threshold value according to the set mode, and the step of determining unnecessary data from the read data of the image reader by comparing the value of the read data of the image reader with the set threshold value.
According to the present invention, unnecessary data is determined from the read data of the image reader according to the comparison result with a threshold value set appropriately corresponding to the mode. Therefore, unnecessary data can be determined appropriately to prevent generation of a black or white streak.
Preferably, the threshold value set step refers to a data table in which a plurality of modes and a threshold value are stored in correspondence to set a threshold value.
Since a data table in which a threshold value is stored corresponding to a mode is referred to, an appropriate threshold value can be set easily.
Preferably, the plurality of modes includes at least one of a plurality of modes set according to the type of the document image, a plurality of modes set according to the amount of exposure of the image reader, and a plurality of modes set according to the type of dust adhering to the image reader.
Accordingly, a threshold value is set corresponding to a parameter that greatly affects detection of dust such as the type of document image, the amount of exposure of the image reader, and the type of dust. Thus, a threshold value can be set more appropriately to prevent generation of a black or white streak.
Preferably, the image reader includes a plurality of fixed read units having a different readout position with respect to the moving direction of the document.
Accordingly, a document is read out by a plurality of fixed read units having a different readout position with respect to the moving direction of the document. Therefore, a plurality of read data can be obtained to determine unnecessary data more appropriately from the obtained data.
Preferably, the read unit includes a line sensor extending in a direction orthogonal to the moving direction of the document.
Accordingly, the document is read out by a plurality of fixed read units having a different readout position with respect to the moving direction of the document. Therefore, a plurality of read data can be obtained, and unnecessary data can be determined more appropriately from the obtained data.